Pyrrolo-2,3-quinodimethanes

In 1984, a facile synthesis of pyrrolo[3,4-/7]indole (5) as a stable indole-2,3-quinodimethane analogue using an intramolecular azide-alkene cycloaddition-cycloreversion strategy was reported (Scheme 9.2) (3). Treatment of bromo compound 3 with NaNs in aqueous tetrahydrofuran (THF) produced the triazoline 4 via an intramolecular 1,3-dipolar cycloaddition of an intermediate azide. Treatment of the triazoline 4 with p-toluenesulfonic acid (p-TSA) effected 1,3-dipolar cycloreversion of 4 to give pyrroloindole 5 in 82% yield along with diethyl diazomalonate. 

A short and novel synthetic route toward pyrrolo-3-sulfolene (189) and its W-mesyl derivative (407), precursors for the corresponding pyrrolo o-quinodimethanes, has been developed. The syn-... 

A pyrrolo[3,4-Z>]indole (320), which can be prepared by an intramolecular aza-Wittig reaction and JV -protection, acts as a quinodimethane and undergoes cycloaddition to 3,4-pyridyne to yield a mixture of isomeric adducts (321) and (322) which are precursors of ellipticine and isoellipticine (Scheme 98) <84CC1552, 92T10645>. 

The pyrrolo[3,4-Z ]indoles offer an alternative approach to access indolo-2,3-quinodimethane analogs and have also been used in Diels-Alder cycloaddition reactions with acetylenes to produce a variety of substituted carbazoles. The most widely used methods developed for the synthesis of pyrrolo[3,4-b]indoles have already been reviewed [126, 127] and thus wiU not be discussed here. 

In addition to the pyrano[3,4- i]indol-3-one ring system, another group of stable indole-2,3-quinodimethane synthetic equivalents are the fused indole ring systems, pyrrolo[3,4-fc]indole, furo[3,4- ]indole, thieno[3,4- ] indole, and seleno[3,4- ]indole, each of which is known. 

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